Gravel pack treatments are frequently conducted in loosely consolidated formations to retain formation particles so hydrocarbonaceous fluids can be produced through the pack. Most gravel packs are placed within a well in conjunction with a slotted liner or wire-wrapped screen. The liner or screen is used to help hold the sand control gravel in place and has small slots of sufficient size to allow production of hydrocarbonaceous fluids through the liner. There are several areas in the world such as the Gulf Coast, offshore California, Canada, and Africa where gravel pack treatments are conducted as a standard operating procedure in well completions.
Although the use of gravel packs is widespread for control of formation sand production, existing methods of evaluating the efficiency of the gravel pack usually depend on observation of hydrocarbon production through the pack. Workover of the pack then requires substantial down time and frequently involves complete removal of the liner and initial gravel pack. These reworks are costly and can result in formation damage due to the loss of kill fluids and additional gravel pack fluid to the formation.
Most successful gravel packs eventually require remedial treatments such as acidizing or solvent washes to remove deposited material from the pack bed to restore permeability to the pack for the production of formation hydrocarbons. It is difficult to ascertain, by existing methods, the reason for the decreased productivity through the pack. However, if an improper remedial treatment is selected, additional damage can occur leading to a further decrease in productivity. Reasons for decreased productivity through an otherwise successful gravel pack include reservoir depletion, accumulation of formation fines and silt, scale buildup from formation water flowing through the pack, and asphaltene and/or paraffin precipitation. Pressure buildup tests are occasionally used in gravel pack evaluation. These tests, conducted carefully using correct procedures, provide an excellent indication of degree of reservoir depletion and will also give information related to the extent of pack damage. However, reservoir pressure tests cannot be used to determine the type of damage in the pack if a "positive skin" is calculated from the measured data.
Therefore, what is needed is a method to determine the efficiency of a gravel pack prior to producing hydrocarbonaceous fluids through said pack. Also, what is needed is a method to ascertain the cause of decreased efficiency in a gravel pack during the production of hydrocarbonaceous fluids so the correct remedial treatment can be instituted.